This invention relates to a micro-manipulation method for handling a micro-object which is designed with excellent repeatability in a microscope that radiates electron beams and uses secondary electron, reflected electron and transmitted electron signals to magnify an object for observation.
To analyze fine foreign particles, to assemble microstructures or to study characteristics of a micro object, it has been necessary to manipulate a micro object with a micro-manipulator attached to a scanning electron microscope (SEM) or a transmission electron microscope (TEM). A relatively large object of about 100 xcexcm in size has been usually gripped by a micro-handling tool that looks like a tweezer and held by frictional force. If an object is as small as about 10 xcexcm, it would not easily be released from a handling tool surface due to specific inter-surface adhesion force acting on the tool surface and the object surface. Moreover, such a micro-object needs not to be gripped because it can be held with enough force only by contacting with a tool. A tweezer-like tool has therefore not very useful with regard to a micro-object.
Conventional techniques have employed a needle-shaped handling tool and used attractive or repulsive electrostatic forces to pick up or release objects while controlling the potentials of the tool and the work substrate. Generally, applying a positive voltage to the handling tool enables pick-up because the object is negatively charged by electron beam irradiation. To place the object on the work substrate, applying a negative voltage to the tool and a positive voltage to the substrate will release the object from the tool with high repeatability.
Conventional techniques enable relatively good repeatability of pick-and-release control when objects are negatively charged by electron beam irradiation, but these techniques have been applicable only under limited conditions.
For example, when a size of an object is as small as several micrometers, its charge state changes and lowers the repeatability of pick-and-release control. When such charge state change occurs, the operation must be repeated for many times to achieve the desired result, or the pick-up and release are completely disabled, making it impossible to accomplish the work.
The object of this invention is to provide a micro-manipulation method for handling a micro-object of several micrometers or less in size and to achieve excellent repeatability, and thereby to solve the above-noted problems.
The technical solution adopted by this invention is as follows:
A micro-manipulation method for handling micro-objects with a micro-handling tool while under the electron beam irradiation of an electron microscope, wherein the accelerating voltage of the electron beam, the potential of the micro-handling tool and the potential of a work substrate are adjusted to enable pick-up and release of micro-objects with the micro-handling tool.
In the micro-manipulation method, the accelerating voltage of an electron beam and the size of a micro-object may have a relationship that makes the electron beam penetrate the micro-object.
Further in the micro-manipulation method, the work substrate may be a conductive glass substrate that is coated with a thin polymer film to increase adhesion forces between the object and the substrate. Further in the micro-manipulation method, the work substrate may be a glass substrate on which a thin ITO (indium Tia oxide) film, or a transparent conductive electrode, is evaporated and a thin polystyrene film is then dip-coated on the top thereof to increase adhesion forces between the object and the substrate.